Along with the trend in recent years in the semiconductor devices toward compact size and high integration, development works were practiced for the use of light sources for the fine working including ultraviolet lights such as the g-line and i-line, excimer laser beams such as KrF and ArF and the like as well as photoresist compositions suitable thereto such as, for example, chemical-amplification photoresist compositions while many of the problems on the lithographic technology in this direction are now on the way of solution.
Meanwhile, one of the problems is pattern falling during formation of a fine resist pattern or, in particular, pattern of a high aspect ratio by the lithographic technology. This pattern falling is a phenomenon encountered in the parallel formation of a large number of patterns on a substrate that adjacent patterns are brought near as if leaning each other eventually leading to breaking or exfoliation of the pattern at the base part. If such pattern falling occurs, desirable products can no longer be obtained resulting in a decrease of the product yield and reliability of the products.
Meanwhile, the reason for this pattern falling has already been elucidated [Japanese Journal of Applied Physics, vol. 32 (1993), p. 6059-p. 6064] and is understood to be caused by the surface tension of the rinse solution acting in the course of drying of the rinse solution during the rinse treatment of the resist pattern after development.
Accordingly, no forces to cause pattern falling are produced when the resist pattern is kept immersed in the rinse solution or, namely, during the rinse treatment after development but, in the course of the drying step to remove the rinse solution, forces due to the surface tension of the rinse solution act between the resist patterns leading to resist falling.
Theoretically, therefore, pattern falling could be prevented by using a rinse solution having a small surface tension or, namely, exhibiting a large contact angle so that it was the attempt heretofore to prevent pattern falling by the admixture of the rinse solution with an additive compound capable of decreasing the surface tension or increasing the contact angle.
For example, proposals were made for a rinse solution with addition of isopropyl alcohol (JP6-163391A), a method in which the contact angle between the resist surface after development and the rinse solution is adjusted to be in the range of 60 to 120 degrees by using a mixture pf isopropyl alcohol and water or isopropyl alcohol and a fluorinated ethylene compound as the rinse solution (JP5-2993363A), a method of using a rinse solution having a surface tension adjusted in the range of 30 to 50 dynes/cm by the addition of an alcohol, a ketone or a carboxylic acid for a resist by using a novolac resin or a hydroxypolystyrene resin as the base material of the resist composition (JP7-140674A), a method of adding a fluorine-containing surfactant to at least one of the developer solution and the rinse solution (JP7-142349A), a method comprising a step of rinse with water and a step of drying after replacement with a water-immiscible liquid having a small surface tension and having a larger specific gravity than water such as, for example, a perfluoroalkyl polyether while the resist is kept immersed in water (JP7-226358A), a rinse agent composition containing a nitrogen-containing compound having a molecular weight of 45 to 10000 and having a hydrocarbon group with 1 to 20 carbon atoms and an amino group, imino group or an ammonium group in the molecule (JP11-295902A), a method of using a composition containing a fluorinated carboxylic acid, fluorinated sulfonic acid or a salt thereof as the developer solution (JP2002-323773A), a method of treatment of the developed substrate with an organic treatment agent containing a hydrofluoroether after a rinse treatment (JP2003-178943A and JP2003-178944A) and elsewhere.
With each of these rinse solutions or the rinse treatment methods, however, it is not possible to completely prevent pattern falling and, in addition, a risk of decrease is caused in the properties or, in particular, the precision of the pattern formed thereby so that they are not always satisfactory for industrialization.
On the other hand, the fluorine-containing surfactant used nowadays is perfluorooctane sulfonic acid (PFOS). This substance has a serious problem in handling because it is a “designated chemical substance” within Japan and also is an objective of the Significant novel utilization rules (SNUR) in the United States as an ecological influences-related rule. To say in particular, since the substances under the SNUR regulations may bring about an unreasonable risk to damage the health or environment necessitating wearing of protectors in the working place and education and training of employees with information on the toxicity and so on with a further regulation on the discarding treatment. It is accordingly desired to obtain a fluorine-based surfactant capable of exhibiting equivalent effects as in the use of the perfluorooctane sulfonic acid and containing a fluorine-based surfactant with good handleableness and without environmental problems to replace the perfluorooctane sulfonic acid.